FIELD OF THE INVENTION
The present invention relates to machines for shearing, bending or working substantially rigid, generally flat materials and, more particularly, to a material working machine having an automatic positioning system for adjusting the back gauge of the machine in preparation for the placement and working of the materials.
Machines for working relatively small flat sheets and other small articles are often hand or foot operated and provided with hand adjusted gauges for centering and/or aligning the articles with respect to the cutting blades, punching dies or bending bar. Alignment is achieved with respect to the working tool of the machine by adjusting a back gauge against which the worked material is positioned. The back gauge is positioned a desired distance from the cutting, punching or bending tool, and the article is cut, punched or bent to the desired adjusted dimension.
Unfortunately, the set-up, aligning, and calibrating of the back gauge of these material working machines, often requires significant adjustment time. It is not unusual, for example, for a skilled worker to spend half an hour adjusting the back gauge of a metal shearing device before the device can consistently shear metal parts to within ten thousandths of an inch of the desired dimension.
Highly accurate, numerically controlled devices have been used in large, automatic machines to position workpieces relative to the cutting or bending members. Such numerically controlled devices generally utilize programmed, feedback systems. Such sophisticated feedback systems are generally too elaborate and expensive for adaptation to small, manually operated machines. These closed-loop control devices are not cost effective for small production runs and/or manually operated material working machines.
One such closed-loop system for generating position signals to a servo control unit for moving the back gauge of a paper cutting machine is disclosed in U.S. Pat. No. 3,738,504, issued to Vail et al. Feedback signals provide binary coded position information associated with key control positions in the back gauge. Pulsed counting information is used to increment position changes in each interval between the key control positions. This closed-loop system utilizes an optical disk and requires feedback inputs. The paper cutting machine is completely automatic, not requiring the intervention of a human operator to initiate the aligning or cutting of the materials. Moreover, the back gauge is automatically adjusted with respect to the cutting blade by means of an AC motor-driven belt.
U.S. Pat. No. 4,280,182, issued to Mickowski, illustrates a typical automatically controlled die stamping device having a microprocessor, a memory, and closed-loop, servo-control circuitry. The computer memory contains data representing the position ordinance of each machine axis, which is utilized in an operational sequence defined by a multiple number of axis-related stamping programs. Binary coded data is used to position the die with respect to the workpiece. The system is completely automatic, requiring no intervention by an operator.
U.S. Pat. No. 4,371,942, issued to Damikolas, discloses a method and apparatus for automatically moving a cutting tool and workpiece into contact with each other. After selecting the material working mode of operation, the cutting tool and workpiece are moved towards each other; when they touch, the cutting tool is separated from the workpiece by a selected distance indicative or the dimension to be cut in the workpiece. Movement between the cutting tool and the workpiece is halted when a sound transducer indicates that contact has been made. In this way, an absolute position of the cutting tool with respect to the workpiece is determined and calibrated. Such a system calibrates the zero position of the workpiece for each article being cut. In other words, the zero position is continuously being readjusted.
Small, manually operated machines, on the other hand, still utilize a rather primitive manual trial and error adjustment mechanism and process. The adjustment mechanism usually consists of an inexpensive dual worm feed mechanism. Each worm feed of the dual worm mechanism is attached to an opposite side of the back gauge upon which the workpiece is aligned. Each one of the dual worm feed units in turn is caused to adjust, by manual means, first one, and then the opposite side of the back gauge. Each worm feed has a adjusting dial nut assembly for setting the position of its respective worm feed unit for adjusting its respective side of the back gauge. Upon aligning first one side of the back gauge, the other one of the dual worm feed units is adjusted in like manner.
Normally, such a system could provide an alignment of both sides of the back gauge with respect to the cutting tool in a few minutes, if it weren't for the problem of worm feed inaccuracy and backlash. All too often, one side must be backed off from its initial setting, when the other side of the back gauge is adjusted. When this happens, the dial nut of the previously adjusted feed unit must be disengaged to allow the feed unit for the first side to be adjusted. Error and backlash in the worm feed units causes a constant inaccuracy to be experienced in readjusting each position, such that the whole adjustment procedure becomes one of trial and error.
Such a trial and error procedure has been tolerated by reason of the fact that the amount of work contemplated for manually operated material working machines is small. Such small production runs do not warrant the expense of installing or utilizing precision worm feeds in such equipment. Particularly when the cost of present automatic adjusting means was appreciable as compared to the cost of the machine itself.
The present invention, while providing an automated system for accurately and precisely setting the back gauge of a manually operated, material working machine, does so without appreciably adding to the cost of the machine.
The invention accomplishes a low cost automatic alignment system by reason of the reduction of mechanical drive parts, together with inexpensive electronic control components. The invention replaces the dual worm feed of the prior art system with a single worm feed, featuring a precision, zero-backlash recirculating ball nut assembly. The worm feed is centered in a mid-portion of the back gauge, thus eliminating the need for alternate side adjustments. The worm feed is automatically driven to a selected position chosen by the operator. A desired back gauge position with respect to a work blade is selected by an operator using a thumbwheel switch or equivalent disposed on an input panel. The input setting is fed to a microprocessor controller that feeds drive signals to a stepper motor. The stepper motor drives the worm feed to a precise setting without using feedback circuitry, in accordance with the input. In other words, the present invention accomplishes low cost precision adjustment utilizing an open-loop circuit.
It is an object of the present invention to provide a low cost system for automatically and accurately positioning a back gauge of a manually operated, material working apparatus.
It is another object of this invention to provide an automatic positioning system featuring an open-loop circuit.
It is another object of the invention to provide a method for rapidly and precisely adjusting the back gauge and/or workpiece relative to a cutting, punching or bending tool without having to use trial and error.